Exhaust aftertreatment system with low-temperature scr

ABSTRACT

An aftertreatment system may treat exhaust gas discharged from an engine. The system may include first and second selective-catalytic-reduction (SCR) catalysts and a valve. The valve may be disposed upstream of the first SCR catalyst and at least one of an oxidation catalyst and a particulate filter. The valve is connected to first and second exhaust flow paths and is movable between a first position allowing exhaust gas to flow through the first flow path and bypass the second flow path and a second position allowing exhaust gas to flow through the second flow path and bypass the first flow path. The second SCR catalyst may be a low-temperature SCR catalyst and may be disposed in the second flow path. A control module may cause the valve to move between the first and second positions based on a temperature of the exhaust gas and/or a temperature of the engine.

FIELD

The present disclosure relates to an exhaust aftertreatment system for acombustion engine.

BACKGROUND

This section provides background information related to the presentdisclosure and is not necessarily prior art.

In an attempt to reduce the quantity of NO_(x) and particulate matteremitted to the atmosphere during internal combustion engine operation, anumber of exhaust aftertreatment devices have been developed. A need forexhaust aftertreatment systems particularly arises when dieselcombustion processes are implemented. Typical aftertreatment systems fordiesel engine exhaust may include one or more of a diesel particulatefilter (DPF), a selective catalytic reduction (SCR) system (including aurea injector), a hydrocarbon (HC) injector, and a diesel oxidationcatalyst (DOC).

Following a cold start of an engine, exhaust gas temperatures are muchlower than exhaust gas temperatures produced by the engine at normaloperating temperatures. For example, cold-start exhaust gas temperaturescan be between approximately 60-250 degrees Celsius. Conventional SCRcatalysts often fail to effectively reduce NO_(x) from such cold-startexhaust gas streams. Therefore, it may be desirable to provide anaftertreatment system with an SCR catalyst that can effectively reduceNO_(x) from cold-start exhaust gas and another SCR catalyst that caneffectively reduce NO_(x) from exhaust gas at normal operatingtemperatures.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

In one form, the present disclosure provides an aftertreatment systemfor treating exhaust gas discharged from a combustion engine. Theaftertreatment system may include first and secondselective-catalytic-reduction catalysts, a valve and a control module.The valve may be disposed upstream of the firstselective-catalytic-reduction catalyst and at least one of an oxidationcatalyst and a particulate filter. The valve may be connected to firstand second exhaust flow paths and may be movable between a firstposition allowing exhaust gas to flow through the first exhaust flowpath and bypass the second exhaust flow path and a second positionallowing exhaust gas to flow through the second exhaust flow path andbypass the first exhaust flow path. The secondselective-catalytic-reduction catalyst may be a low-temperatureselective-catalytic-reduction catalyst and may be disposed in the secondexhaust flow path. The control module is in communication with the valveand may be configured to cause the valve to move between the first andsecond positions based on at least one of a temperature of the exhaustgas and a temperature of the combustion engine.

In some embodiments, the first and second exhaust flow paths aredisposed upstream of the at least one of the at least one of theoxidation catalyst and particulate filter.

In some embodiments, the first and second exhaust flow paths aredisposed upstream of the first selective-catalytic-reduction catalyst.

In some embodiments, the second exhaust flow path includes a fluidinjection port (e.g., a port through which urea, ammonia or any otherreagent can be injected into the exhaust stream) disposed upstream ofthe second selective-catalytic-reduction catalyst.

In some embodiments, the aftertreatment system includes another fluidinjection port disposed between the first selective-catalytic-reductioncatalyst and the at least one of the oxidation catalyst and theparticulate filter.

In some embodiments, the at least one of the oxidation catalyst andparticulate filter is disposed in the first exhaust flow path.

In some embodiments, the aftertreatment system includes an oxidationcatalyst and a particulate filter disposed directly adjacent and/orproximate to each other.

In some embodiments, the first selective-catalytic-reduction catalyst isdisposed in the first exhaust flow path.

In some embodiments, the aftertreatment system includes an ammonia gasgenerator disposed upstream of at least one of the first and secondselective-catalytic-reduction catalysts.

In another form, the present disclosure provides an aftertreatmentsystem that may include first and second injection ports, first andsecond selective-catalytic-reduction catalysts, and at least one of anoxidation catalyst and a particulate filter. Reagent may be injectedinto the exhaust stream through the first injection port. The firstselective-catalytic-reduction catalyst may be disposed downstream of thefirst injection port. The first selective-catalytic-reduction catalystmay be a low-temperature selective-catalytic-reduction catalyst. Theoxidation catalyst and/or particulate filter may be disposed downstreamof the low-temperature selective-catalytic-reduction catalyst. Reagentmay be injected into the exhaust stream through the second injectionport downstream of the oxidation catalyst and/or the particulate filter.The second selective-catalytic-reduction catalyst may be disposeddownstream of the second injection port.

The first and second injection ports can be or include a DEF dosingsystem or urea or ammonia injector, nozzle or other orifice throughwhich reagent can be injected into the exhaust stream.

In some embodiments, the aftertreatment system may include alow-temperature flow path, a bypass flow path, and a valve. Thelow-temperature flow path may include the firstselective-catalytic-reduction catalyst. The bypass flow path may beisolated from the first selective-catalytic-reduction catalyst. Thevalve may be disposed upstream of the secondselective-catalytic-reduction catalyst and may be movable between afirst position allowing exhaust gas to flow through the low-temperatureflow path and preventing exhaust gas from flowing through the bypassflow path and a second position allowing exhaust gas to flow through thebypass flow path and preventing exhaust gas from flowing through thelow-temperature flow path.

In some embodiments, reagent is injected into the low-temperature flowpath through the first injection port.

In some embodiments, the low-temperature flow path and the bypass flowpath are disposed upstream of the at least one of the oxidation catalystand particulate filter.

In some embodiments, the aftertreatment system includes a control modulein communication with the valve and configured to cause the valve tomove between the first and second positions based on at least one of atemperature of the exhaust gas and a temperature of the combustionengine.

In some embodiments, the bypass flow path includes the secondselective-catalytic-reduction catalyst.

In some embodiments, the bypass flow path includes the second injectionport.

In some embodiments, the aftertreatment system includes an ammonia gasgenerator disposed upstream of at least one of the first and secondselective-catalytic-reduction catalysts.

In another form, the present disclosure provides an aftertreatmentsystem that may include a low-temperature flow path, a bypass flow pathand a valve. The low-temperature flow path may include a firstselective-catalytic-reduction catalyst. The bypass flow path may includea second selective-catalytic-reduction catalyst. The bypass flow pathmay be isolated from the first selective-catalytic-reduction catalyst.The valve may be configured to receive exhaust gas from the combustionengine. The valve may be movable between a first position allowingexhaust gas to flow through the low-temperature flow path and preventingexhaust gas from flowing through the bypass flow path and a secondposition allowing exhaust gas to flow through the bypass flow path andpreventing exhaust gas from flowing through the low-temperature flowpath.

In some embodiments, the aftertreatment system includes a control modulein communication with the valve and configured to cause the valve tomove between the first and second positions based on at least one of atemperature of the exhaust gas and a temperature of the combustionengine.

In some embodiments, the aftertreatment system may include an oxidationcatalyst and a particulate filter disposed upstream of the secondselective-catalytic-reduction catalyst.

In some embodiments, the oxidation catalyst and the particulate filterare disposed upstream of the valve.

In some embodiments, the aftertreatment system includes another valvedisposed upstream of the oxidation catalyst and the particulate filterand movable between a first position allowing exhaust gas to flowthrough the oxidation catalyst and the particulate filter and a secondposition allowing exhaust gas to flow through another flow path that isisolated from the oxidation catalyst and the particulate filter.

In some embodiments, the aftertreatment system includes an ammonia gasgenerator disposed upstream of at least one of the first and secondselective-catalytic-reduction catalysts.

In another form, the present disclosure provides an aftertreatmentsystem that may include first and second selective-catalytic-reductioncatalysts and a control valve. The second selective-catalytic-reductioncatalyst may be in fluid communication with the firstselective-catalytic-reduction catalyst. The control valve may be incommunication with the first and second selective-catalytic-reductioncatalysts. The control valve may be movable between a first positioncausing exhaust gas to flow through the firstselective-catalytic-reduction catalyst before flowing through the secondselective-catalytic-reduction catalyst and a second position causingexhaust gas to flow through the second selective-catalytic-reductioncatalyst before flowing through the first selective-catalytic-reductioncatalyst.

In some embodiments, the aftertreatment system includes a control modulein communication with the valve. The control module may be configured tocause the control valve to move between the first and second positionsbased on at least one of a temperature of the exhaust gas and atemperature of the combustion engine.

In some embodiments, the aftertreatment system includes an oxidationcatalyst disposed upstream of the control valve.

In some embodiments, the aftertreatment system includes a particulatefilter disposed upstream of the control valve.

In some embodiments, the aftertreatment system includes a downstreamvalve configured to receive exhaust gas after the exhaust gas has flowedthrough the first and second selective-catalytic-reduction catalysts.

In some embodiments, the downstream valve is movable between a firstposition allowing exhaust gas from the secondselective-catalytic-reduction catalyst to flow through the downstreamvalve and preventing exhaust gas from flowing from the downstream valveto the first selective-catalytic-reduction catalyst and a secondposition allowing exhaust gas from the firstselective-catalytic-reduction catalyst to flow through the downstreamvalve and preventing exhaust gas from flowing from the downstream valveto the second selective-catalytic-reduction catalyst.

In some embodiments, the aftertreatment system includes a control modulethat moves the downstream valve into its first position and the controlvalve into its first position substantially simultaneously. The controlmodule may also move the downstream valve into its second position andthe control valve into its second position substantially simultaneously.

In some embodiments, the aftertreatment system includes an ammonia gasgenerator disposed upstream of at least one of the first and secondselective-catalytic-reduction catalysts.

In another form, the present disclosure provides an aftertreatmentsystem for treating exhaust gas discharged from a combustion engine. Theaftertreatment system may include first and second exhaust gas flowpaths and first and second selective-catalytic-reduction catalysts. Thefirst exhaust gas flow path may receive a first portion of the exhaustgas from the combustion engine. The first exhaust gas flow path mayinclude an ammonia generator and an injection port through which areagent is injected into the exhaust gas. The second exhaust gas flowpath may receive a second portion of the exhaust gas from the combustionengine and may include at least one of a oxidation catalyst and aparticulate filter. The first and second exhaust gas flow paths may befluidly isolated from each other. The firstselective-catalytic-reduction catalyst may receive exhaust gas from thefirst and second exhaust gas flow paths. The secondselective-catalytic-reduction catalyst may receive exhaust gas from thefirst and second exhaust gas flow paths. The secondselective-catalytic-reduction catalyst may be a low-temperatureselective-catalytic-reduction catalyst.

In some embodiments, the second selective-catalytic-reduction catalystis disposed downstream of the first selective-catalytic-reductioncatalyst.

In some embodiments, the second selective-catalytic-reduction catalystis disposed upstream of the first selective-catalytic-reductioncatalyst.

In some embodiments, the first exhaust gas flow path includes an inletdisposed downstream of a turbocharger.

In some embodiments, the first exhaust gas flow path includes an inletdisposed upstream of a turbocharger.

In some embodiments, the injection port is disposed downstream of theammonia generator.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a schematic representation of an engine and aftertreatmentsystem according to the principles of the present disclosure;

FIG. 2 is a schematic representation of another aftertreatment systemaccording to the principles of the present disclosure;

FIG. 3 is a schematic representation of yet another aftertreatmentsystem according to the principles of the present disclosure;

FIG. 4 is a schematic representation of yet another aftertreatmentsystem according to the principles of the present disclosure;

FIG. 5 is a schematic representation of yet another aftertreatmentsystem according to the principles of the present disclosure; and

FIG. 6 is a schematic representation of yet another aftertreatmentsystem according to the principles of the present disclosure.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto,” “directly connected to,” or “directly coupled to” another elementor layer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

FIG. 1 depicts an exhaust gas aftertreatment system 10 for treating theexhaust output from an exemplary engine 12 to an exhaust passageway 14.A turbocharger 16 includes a driven member (not shown) positioned in anexhaust stream. During engine operation, the exhaust stream causes thedriven member to rotate and provide compressed air to an intake passage(not shown) of the engine 12. It will be appreciated that the exhaustgas aftertreatment system 10 can also be used to treat exhaust outputfrom a naturally aspirated engine or any other engine that does notinclude a turbocharger.

The exhaust aftertreatment system 10 may include a control valve 18, abypass flow path 20, a low-temperature-treatment flow path 22, a firstinjector or injection port 24 (e.g., a diesel exhaust fluid (DEF) dosingsystem or urea or ammonia injector, nozzle or other orifice throughwhich reagent can be injected into the exhaust stream), a firstselective-catalytic-reduction (SCR) catalyst 26, a diesel oxidationcatalyst (DOC) 28, a diesel particulate filter (DPF) 30, a secondinjector or injection port 32 (e.g., a DEF dosing system or urea orammonia injector, nozzle or other orifice through which reagent can beinjected into the exhaust stream), and a second SCR catalyst 34. Thelow-temperature-treatment flow path 22 may include the first injector 24and the first SCR catalyst 26. The first injector 24 may inject agaseous ammonia, for example, or any other reagent into the exhauststream upstream of the first SCR catalyst 26. The first injector 24 maybe disposed directly or indirectly adjacent and/or proximate to thefirst SCR catalyst 26.

The first SCR catalyst 26 may be a low-temperature SCR catalystconfigured to effectively reduce NO_(x) from low-temperature exhaust gas(e.g., exhaust gas at 60-150 degrees Celsius or 60-250 degrees Celsius)that may be discharged from the engine 12 for a period of time followinga cold start of the engine 12. For example, the first SCR catalyst 26may include a metal oxide supported on titanium oxide (MO_(x)/TiO₂), ametal oxide supported on a titania-silica (TiO₂/SiO₂) mixed oxidesupport, or a metal oxide supported on a beta zeolite. Metals used forsuch catalysts could include ammonium metavenadate (V), manganese (Mn),iron (Fe), cobalt (Co), copper (Cu) or cerium (Ce), for example. Themetals may be loaded onto the TiO₂ support or the TiO₂/SiO₂ support by awet-impregnation method, for example. The metals may be loaded onto thebeta zeolite by a cation exchange method, for example. It will beappreciated that any suitable low-temperature SCR catalyst capable ofeffectively treating low-temperature exhaust gas could be employed.

Exhaust flowing through the bypass flow path 20 bypasses the firstinjector 24 and the first SCR catalyst 26. The control valve 18 mayreceive exhaust gas from the engine 12 and turbocharger 16 and may bemovable between first and second positions. In the first position, thecontrol valve 18 allows exhaust gas to flow through thelow-temperature-treatment flow path 22 and restricts or prevents exhaustgas from flowing through the bypass flow path 20. In the secondposition, the control valve 18 allows exhaust gas to flow through thebypass flow path 20 and prevents exhaust gas from flowing through thelow-temperature-treatment flow path 22. In some configurations, thecontrol valve 18 may be movable to one or more intermediate positionsbetween the first and second positions to allow a portion of the exhaustgas to flow through the bypass flow path 20 and another portion of theexhaust gas to flow through the low-temperature treatment flow path 22.

A control module 36 may control movement of the control valve 18 basedon a temperature of the exhaust gas discharged from the engine 12(measured by a temperature sensor in the exhaust stream), a temperatureof engine coolant (measured by an engine coolant temperature sensor)and/or a runtime of the engine 12, for example. The control module 36may cause the control valve 18 to move into the first position when theexhaust temperature or coolant temperature is below a predeterminedvalue (between about 150 or 250 degrees Celsius, for example). Thecontrol module 36 may cause the control valve 18 to move into the secondposition once the exhaust temperature or coolant temperature rises abovethe predetermined value.

The control module 36 may include or be part of an Application SpecificIntegrated Circuit (ASIC); a digital, analog, or mixed analog/digitaldiscrete circuit; a digital, analog, or mixed analog/digital integratedcircuit; a combinational logic circuit; a field programmable gate array(FPGA); a processor (shared, dedicated, or group) that executes code;memory (shared, dedicated, or group) that stores code executed by aprocessor; other suitable hardware components that provide the describedfunctionality; or a combination of some or all of the above, such as ina system-on-chip. The control module 36 may be a part of or include acontrol unit controlling one or more other vehicle systems.Alternatively, the control module 36 may be a control unit dedicated tothe exhaust aftertreatment system 10. The control module 36 may be incommunication with and control operation of the control valve 18, theinjectors 24, 32 and/or other aftertreatment components.

The DOC 28, the DPF 30, the second injector 32 and the second SCRcatalyst 34 may be disposed downstream of the bypass flow path 20 andthe low-temperature-treatment flow path 22. The DPF 30 may be disposeddownstream of the DOC 28. The DPF 30 may be disposed directly orindirectly adjacent and/or proximate to the DOC 28. The second injector32 may be disposed downstream of the DPF 30 and upstream of the secondSCR catalyst 34. The second injector 32 may be disposed directly orindirectly adjacent and/or proximate to the second SCR catalyst 34. Thesecond SCR catalyst 34 may be a normal-to-high-temperature SCR catalystconfigured to effectively reduce NO_(x) from normal-to-high-temperatureexhaust gas (e.g., exhaust approximately equal to or greater than about150 degrees Celsius, or approximately equal to or greater than about 250degrees Celsius) that may be discharged from the engine 12 under normaland/or high-load operating conditions.

With reference to FIG. 2, another aftertreatment system 110 is providedthat may treat the exhaust gas discharged from the engine 12. Theaftertreatment system 110 may include a DOC 128, a DPF 130, an injectoror injection port 124, a control valve 118, a low-temperature SCRcatalyst 132, a normal-to-high-temperature SCR catalyst 134, and acontrol module 136. The structure and function of the DOC 128, DPF 130,injector 124, SCR catalysts 132, 134, and control module 136 may besimilar or identical to that of the DOC 28, DPF 30, injector 24,32, SCRcatalysts 26, 34, and control module 36, respectively, apart from anyexceptions described below and/or shown in the figures. Therefore,similar features will not be described again in detail.

The DOC 128 may receive exhaust gas from the engine 12 and turbocharger16. The DPF 130 may be disposed downstream of the DOC 128. The injector124 may inject ammonia (or another reagent) into the exhaust streamdownstream of the DPF 130 and upstream of the control valve 118. Thecontrol valve 118 may be fluidly coupled to the low-temperature SCRcatalyst 132 and the normal-to-high-temperature SCR catalyst 134. Thelow-temperature SCR catalyst 132 and the normal-to-high-temperature SCRcatalyst 134 may be fluidly coupled to each other.

The control module 136 may cause the control valve 118 to move betweenfirst and second positions. In the first position, fluid receivedthrough an inlet 119 of the control valve 118 is routed along a firstflow path 140 (indicated in dashed lines in FIG. 2) in which the fluidflows from the control valve 118 to the low-temperature SCR catalyst132, then to the normal-to-high-temperature SCR catalyst 134, then backto the control valve 118. The fluid then exits the control valve 118through an outlet 121 before being discharged into the ambientenvironment. When the control valve 118 is in the second position, fluidreceived through the inlet 119 of the control valve 118 is routed alonga second flow path 142 (indicated in solid lines in FIG. 2) in which thefluid flows from the control valve 118 to the normal-to-high-temperatureSCR catalyst 134, then to the low-temperature SCR catalyst 132, thenback to the control valve 118. The fluid then exits the control valve118 through the outlet 121 before being discharged into the ambientenvironment.

As described above, the control module 136 may control movement of thecontrol valve 118 based on a temperature of the exhaust gas dischargedfrom the engine 12, a temperature of engine coolant and/or a runtime ofthe engine 12, for example. The control module 136 may cause the controlvalve 118 to move into the first position when the exhaust temperatureor coolant temperature is below a predetermined value (between about 150or 250 degrees Celsius, for example). The control module 136 may causethe control valve 118 to move into the second position once the exhausttemperature or coolant temperature rises above the predetermined value.

With reference to FIG. 3, another aftertreatment system 210 is providedthat may treat the exhaust gas discharged from the engine 12. Theaftertreatment system 210 may include a DOC 228, a DPF 230, an injectoror injection port 224, a first control valve 218, a second control valve220, a low-temperature SCR catalyst 232, a normal-to-high-temperatureSCR catalyst 234, and a control module 236. The structure and functionof the DOC 228, DPF 230, injector 224, SCR catalysts 232, 234, andcontrol module 236 may be similar or identical to that of the DOC 28,DPF 30, injector 24,32, SCR catalysts 26, 34, and control module 36,respectively, apart from any exceptions described below and/or shown inthe figures. Therefore, similar features will not be described again indetail.

The DOC 228 may receive exhaust gas from the engine 12 and turbocharger16. The DPF 230 may be disposed downstream of the DOC 228. The injector224 may inject ammonia (or other reagent) into the exhaust streamdownstream of the DPF 230 and upstream of the first control valve 218.The first control valve 218 may be fluidly coupled to thelow-temperature SCR catalyst 232 and the normal-to-high-temperature SCRcatalyst 234. The low-temperature SCR catalyst 232 and thenormal-to-high-temperature SCR catalyst 234 may be fluidly coupled toeach other. The second control valve 220 may be fluidly coupled to thelow-temperature SCR catalyst 232 and the normal-to-high-temperature SCRcatalyst 234.

The control module 236 may cause the first and second control valves218, 220 to move substantially simultaneously between first and secondpositions. When the control valves 218, 220 are in the first position,fluid received through an inlet 219 of the first control valve 218 isrouted out of the first control valve 218 through a first outlet 221along a first flow path 240 (indicated in dashed lines in FIG. 3) to thelow-temperature SCR catalyst 232. From the low-temperature SCR catalyst232, the fluid flows to the normal-to-high-temperature SCR catalyst 234,and then into a first inlet 223 of the second control valve 220. Thefluid then exits the second control valve 220 through an outlet 225before being discharged into the ambient environment. When the controlvalves 218, 220 are in the second position, fluid received through theinlet 219 of the first control valve 218 is routed out of the firstcontrol valve 218 through a second outlet 227 along a second flow path242 (indicated in solid lines in FIG. 3) to thenormal-to-high-temperature SCR catalyst 234. From thenormal-to-high-temperature SCR catalyst 234, the fluid flows to thelow-temperature SCR catalyst 232, and then into a second inlet 229 ofthe second control valve 220. The fluid then exits the second controlvalve 220 through the outlet 225 before being discharged into theambient environment.

As described above, the control module 236 may control movement of thevalves 218, 220 based on a temperature of the exhaust gas dischargedfrom the engine 12, a temperature of engine coolant and/or a runtime ofthe engine 12, for example. The control module 236 may cause the valves218, 220 to move into the first position when the exhaust temperature orcoolant temperature is below a predetermined value (between about 150 or250 degrees Celsius, for example). The control module 236 may cause thevalves 218, 220 to move into the second position once the exhausttemperature or coolant temperature rises above the predetermined value.

With reference to FIG. 4, another aftertreatment system 310 is providedthat may treat the exhaust gas discharged from the engine 12. Theaftertreatment system 310 may include a first injector or injection port324, a low-temperature SCR catalyst 326, a DOC 328, a DPF 330, a secondinjector or injection port 332 and a normal-to-high-temperature SCRcatalyst 334. The structure and function of the injectors 324, 332, theSCR catalysts 326, 334, the DOC 328 and the DPF 330 may be similar oridentical to that of the injectors 24, 32, the SCR catalysts 26, 34, theDOC 28 and the DPF 30, respectively, apart from any exceptions describedbelow and/or shown in the figures. Therefore, similar features will notbe described again in detail.

The first injector 324 may inject ammonia (or any other reagent) intothe exhaust stream downstream of the engine 12 and turbocharger 16. Thelow-temperature SCR catalyst 326 may be disposed downstream of the firstinjector 324 and may be disposed directly or indirectly adjacent and/orproximate to the first injector 324. The DOC 328 may be disposeddownstream of the low-temperature SCR catalyst 326. The DPF 330 may bedisposed downstream of the DOC 328 and may be directly or indirectlyadjacent and/or proximate to the DOC 328. The second injector 332 may bedisposed downstream of the DPF 330 and upstream of thenormal-to-high-temperature SCR catalyst 334. The second injector 332 maybe directly or indirectly adjacent and/or proximate to thenormal-to-high-temperature SCR catalyst 334.

With reference to FIG. 5, another aftertreatment system 410 is providedthat may treat the exhaust gas discharged from the engine 12. Theaftertreatment system 410 may include a first control valve 418, abypass flow path 420, a low-temperature-treatment flow path 422, and asecond control valve 424. A control module 426 may be in communicationwith and control operation of the first and second control valves 418,424. The structure and function of the control module 426 may be similaror identical to that of the control module 36 described above, apartfrom any exceptions described herein and/or shown in the figures.

The bypass flow path 420 may be in fluid communication with the firstand second control valves 418, 424 and may include a DOC 428, a DPF 430,a first injector or injection port 432, and a normal-to-high-temperatureSCR catalyst 434. The DOC 428 and DPF 430 may be disposed between thefirst and second control valves 418, 424 and may be directly orindirectly adjacent and/or proximate to each other. The first injector432 may inject ammonia (or another reagent) downstream of the DPF 430and upstream of the second control valve 424. Thenormal-to-high-temperature SCR catalyst 434 may be disposed downstreamof the second control valve 424. The structure and function of the DOC428, the DPF 430, the first injector 432, and thenormal-to-high-temperature SCR catalyst 434 may be similar or identicalto that of the DOC 28, the DPF 30, the second injector 32, and thesecond SCR catalyst 34, respectively, apart from any exceptionsdescribed herein and/or shown in the figures.

The low-temperature-treatment flow path 422 may be in fluidcommunication with the first and second control valves 418, 424 and mayinclude a second injector or injection port 436 and a low-temperatureSCR catalyst 438. The structure and function of the second injector 436and the low-temperature SCR catalyst 438 may be similar or identical tothat of the injector 24 and low-temperature SCR catalyst 26,respectively, apart from any exceptions described herein and/or shown inthe figures. Therefore, similar features will not be described again indetail. Briefly, the second injector 436 may inject gaseous ammonia, forexample, and/or another reagent into the exhaust stream in thelow-temperature-treatment flow path 422 between the first and secondcontrol valves 418, 424. The low-temperature SCR catalyst 438 may bedisposed downstream of the second control valve 424.

The control module 426 may move the first and second control valves 418,424 substantially simultaneously between first and second positions.When the control valves 418, 424 are in the first position, fluidreceived through an inlet 419 of the first control valve 418 is routedout of the first control valve 418 through a first outlet 421 and intothe low-temperature-treatment flow path 422. As described above, thesecond injector 436 may inject reagent into thelow-temperature-treatment flow path 422 between the first and secondcontrol valves 424. Then, the exhaust stream may flow into a first inlet423 of the second control valve 424 and exit the second control valve424 through a first outlet 425. From the first outlet 425, the exhaustmay flow through the low-temperature SCR catalyst 438 before beingdischarged to the ambient environment. The low-temperature-treatmentflow path 422 may bypass the DOC 428, the DPF 430, the first injector432 and the normal-to-high-temperature SCR catalyst 434.

When the control valves 418, 424 are in the second position, fluidreceived through the inlet 419 of the first control valve 418 is routedout of the first control valve 418 through a second outlet 427 and intothe bypass flow path 420. From the second outlet 427, the fluid may flowthrough the DOC 428 and through the DPF 430 before reagent is injectedinto the exhaust stream by the first injector 432. Thereafter, theexhaust may flow into the second control valve 424 through a secondinlet 429 and out of the second control valve 424 through a secondoutlet 431. From the second outlet 431, the exhaust may flow through thenormal-to-high-temperature SCR catalyst 434 before being discharged intothe ambient environment.

As described above, the control module 426 may control movement of thecontrol valves 418, 424 based on a temperature of the exhaust gasdischarged from the engine 12, a temperature of engine coolant and/or aruntime of the engine 12, for example. The control module 426 may causethe control valves 418, 424 to move into the first position when theexhaust temperature or coolant temperature is below a predeterminedvalue (between about 150 or 250 degrees Celsius, for example). Thecontrol module 426 may cause the control valves 418, 424 to move intothe second position once the exhaust temperature or coolant temperaturerises above the predetermined value.

In some configurations, the control module 426 may, under certainconditions, cause the first control valve 418 to be in the firstposition while the second control valve 424 is in the second position.While the control valves 418, 424 are in such positions, the exhaust gasmay flow from the first control valve 418 through an upstream portion ofthe low-temperature-treatment flow path 422 (bypassing the DOC 428, theDPF 430 and first injector 432) and out of the second outlet 431 of thesecond control valve 424 to the normal-to-high-temperature SCR catalyst434 before being discharged to the ambient environment.

In some configurations, the control module 426 may, under certainconditions, cause the first control valve 418 to be in the secondposition while the second control valve 424 is in the first position.While the control valves 418, 424 are in such positions, the exhaust gasmay flow from the first control valve 418 through the DOC 428 and theDPF 430. From the DPF 430, the exhaust stream may flow into the secondcontrol valve 424 and exit the second control valve 424 through thefirst outlet 425. From the first outlet 425, the exhaust may flowthrough the low-temperature SCR catalyst 438 before being discharged tothe ambient environment.

With reference to FIG. 6, another aftertreatment system 510 is providedthat may treat the exhaust gas discharged from the engine 12. Theaftertreatment system 510 may include a first exhaust gas flow path 512,a second exhaust gas flow path 514, a normal-to-high-temperature SCRcatalyst 516 and a low-temperature SCR catalyst 518. While FIG. 6depicts the normal-to-high-temperature SCR catalyst 516 being upstreamof the low-temperature SCR catalyst 518, in some embodiments,low-temperature SCR catalyst 518 may be disposed upstream of thenormal-to-high-temperature SCR catalyst 516. The structure and functionof the SCR catalysts 516, 518 may be similar or identical to that of theSCR catalysts 34, 26, respectively, apart from any exceptions describedbelow and/or shown in the figures. Therefore, similar features will notbe described again in detail.

The first exhaust gas flow path 512 may include an ammonia gas generator520 and an injector or injection port 522 (e.g., an injector, nozzleand/or other orifice through which reagent can be injected into theexhaust stream). FIG. 6 shows an inlet 524 of the first exhaust gas flowpath 512 disposed downstream of the turbocharger 16. In someembodiments, however, the inlet 526 may be upstream of the turbocharger16 so that fluid flowing through the first exhaust gas flow path 512bypasses the turbocharger 16. The ammonia gas generator 520 may receiveexhaust gas and convert urea (or another compound containing ammonia) togaseous ammonia (or a gas containing ammonia). An outlet 526 of thefirst exhaust gas flow path 512 may be disposed upstream of the SCRcatalysts 516, 518 such that the injector 522 may feed the exhaust andgaseous ammonia to the SCR catalysts 516, 518.

The second exhaust gas flow path 514 may include a DOC 528 and a DPF530. The DOC 528 and DPF 530 may be disposed between the inlet 524 andoutlet 526 of the first exhaust gas flow path 512. The DOC 528 may beupstream or downstream of the DPF 530. The structure and function of theDOC 528 and DPF 530 may be similar or identical to that of the DOC 28and DPF 30 described above.

It will be appreciated that any of the aftertreatment systems 10, 110,210, 310, 410 described above may include an exhaust flow path similaror identical to the first exhaust gas flow path 512 (e.g., including theammonia gas generator 520 and/or injector or injection port 522) thatmay bypass the DOC, DPF and/or one or more other components of theaftertreatment system 10, 110, 210, 310, 410.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

1. An aftertreatment system for treating exhaust gas discharged from acombustion engine, the aftertreatment system comprising: at least one ofan oxidation catalyst and a particulate filter configured to receiveexhaust gas; first and second selective-catalytic-reduction catalysts; avalve disposed upstream of the first selective-catalytic-reductioncatalyst and the at least one of the oxidation catalyst and particulatefilter, the valve connected to first and second exhaust flow paths andmovable between a first position allowing exhaust gas to flow throughthe first exhaust flow path and bypass the second exhaust flow path anda second position allowing exhaust gas to flow through the secondexhaust flow path and bypass the first exhaust flow path, the secondselective-catalytic-reduction catalyst is a low-temperatureselective-catalytic-reduction catalyst and is disposed in the secondexhaust flow path; and a control module in communication with the valveand configured to cause the valve to move between the first and secondpositions based on an operating parameter of the combustion engine. 2.The aftertreatment system of claim 1, wherein the first and secondexhaust flow paths are disposed upstream of the at least one of theoxidation catalyst and particulate filter.
 3. The aftertreatment systemof claim 2, wherein the first and second exhaust flow paths are disposedupstream of the first selective-catalytic-reduction catalyst.
 4. Theaftertreatment system of claim 1, wherein the second exhaust flow pathincludes a fluid injection port disposed upstream of the secondselective-catalytic-reduction catalyst.
 5. The aftertreatment system ofclaim 4, further comprising another fluid injection port disposedbetween the first selective-catalytic-reduction catalyst and the atleast one of the oxidation catalyst and the particulate filter.
 6. Theaftertreatment system of claim 1, wherein the at least one of theoxidation catalyst and particulate filter is disposed in the firstexhaust flow path.
 7. The aftertreatment system of claim 6, wherein thefirst selective-catalytic-reduction catalyst is disposed in the firstexhaust flow path.
 8. An aftertreatment system for treating exhaust gasdischarged from a combustion engine, the aftertreatment systemcomprising: a first injection port through which reagent is injectedinto an exhaust stream; a first selective-catalytic-reduction catalystdisposed downstream of the first injection port, the firstselective-catalytic-reduction catalyst is a low-temperatureselective-catalytic-reduction catalyst; at least one of an oxidationcatalyst and a particulate filter disposed downstream of thelow-temperature selective-catalytic-reduction catalyst; a secondinjection port through which reagent is injected into the exhaust streamdownstream of the at least one of the oxidation catalyst and particulatefilter; and a second selective-catalytic-reduction catalyst disposeddownstream of the second injection port.
 9. The aftertreatment system ofclaim 8, further comprising: a low-temperature flow path including thefirst selective-catalytic-reduction catalyst; a bypass flow pathisolated from the first selective-catalytic-reduction catalyst; and avalve disposed upstream of the second selective-catalytic-reductioncatalyst and movable between a first position allowing exhaust gas toflow through the low-temperature flow path and preventing exhaust gasfrom flowing through the bypass flow path and a second position allowingexhaust gas to flow through the bypass flow path and preventing exhaustgas from flowing through the low-temperature flow path.
 10. Theaftertreatment system of claim 9, wherein the first injection portprovides reagent to the low-temperature flow path.
 11. Theaftertreatment system of claim 10, wherein the low-temperature flow pathand the bypass flow path are disposed upstream of the at least one ofthe oxidation catalyst and particulate filter.
 12. The aftertreatmentsystem of claim 9, further comprising a control module in communicationwith the valve and configured to cause the valve to move between thefirst and second positions based on an operating parameter of thecombustion engine.
 13. The aftertreatment system of claim 9, wherein thebypass flow path includes the second selective-catalytic-reductioncatalyst.
 14. The aftertreatment system of claim 13, wherein the bypassflow path includes the second injection port.
 15. An aftertreatmentsystem for treating exhaust gas discharged from a combustion engine, theaftertreatment system comprising: a low-temperature flow path includinga first selective-catalytic-reduction catalyst; a bypass flow pathincluding a second selective-catalytic-reduction catalyst, the bypassflow path isolated from the first selective-catalytic-reductioncatalyst; and a valve configured to receive exhaust gas from thecombustion engine and movable between a first position allowing exhaustgas to flow through the low-temperature flow path and preventing exhaustgas from flowing through the bypass flow path and a second positionallowing exhaust gas to flow through the bypass flow path and preventingexhaust gas from flowing through the low-temperature flow path.
 16. Theaftertreatment system of claim 15, further comprising a control modulein communication with the valve and configured to cause the valve tomove between the first and second positions based on an operatingparameter of the combustion engine.
 17. The aftertreatment system ofclaim 15, further comprising an oxidation catalyst and a particulatefilter disposed upstream of the second selective-catalytic-reductioncatalyst.
 18. The aftertreatment system of claim 17, wherein theoxidation catalyst and the particulate filter are disposed upstream ofthe valve.
 19. The aftertreatment system of claim 18, further comprisinganother valve disposed upstream of the oxidation catalyst and theparticulate filter and movable between a first position allowing exhaustgas to flow through the oxidation catalyst and the particulate filterand a second position allowing exhaust gas to flow through another flowpath that is isolated from the oxidation catalyst and the particulatefilter.
 20. The aftertreatment system of claim 15, further comprising anammonia gas generator disposed upstream of at least one of the first andsecond selective-catalytic-reduction catalysts.
 21. An aftertreatmentsystem for treating exhaust gas discharged from a combustion engine, theaftertreatment system comprising: a first selective-catalytic-reductioncatalyst; a second selective-catalytic-reduction catalyst in fluidcommunication with the first selective-catalytic-reduction catalyst; acontrol valve in communication with the first and secondselective-catalytic-reduction catalysts and movable between a firstposition causing exhaust gas to flow through the firstselective-catalytic-reduction catalyst before flowing through the secondselective-catalytic-reduction catalyst and a second position causingexhaust gas to flow through the second selective-catalytic-reductioncatalyst before flowing through the first selective-catalytic-reductioncatalyst.
 22. The aftertreatment system of claim 21, further comprisinga control module in communication with the valve and configured to causethe control valve to move between the first and second positions basedon an operating parameter of the combustion engine.
 23. Theaftertreatment system of claim 21, further comprising an oxidationcatalyst disposed upstream of the control valve.
 24. The aftertreatmentsystem of claim 21, further comprising a particulate filter disposedupstream of the control valve.
 25. The aftertreatment system of claim21, further comprising a downstream valve configured to receive exhaustgas after the exhaust gas has flowed through the first and secondselective-catalytic-reduction catalysts.
 26. The aftertreatment systemof claim 25, wherein the downstream valve is movable between a firstposition allowing exhaust gas from the secondselective-catalytic-reduction catalyst to flow through the downstreamvalve and preventing exhaust gas from flowing from the downstream valveto the first selective-catalytic-reduction catalyst and a secondposition allowing exhaust gas from the firstselective-catalytic-reduction catalyst to flow through the downstreamvalve and preventing exhaust gas from flowing from the downstream valveto the second selective-catalytic-reduction catalyst.
 27. Theaftertreatment system of claim 26, further comprising a control modulethat moves the downstream valve into its first position and the controlvalve into its first position substantially simultaneously and moves thedownstream valve into its second position and the control valve into itssecond position substantially simultaneously.
 28. The aftertreatmentsystem of claim 21, further comprising an ammonia gas generator disposedupstream of at least one of the first and secondselective-catalytic-reduction catalysts.
 29. An aftertreatment systemfor treating exhaust gas discharged from a combustion engine, theaftertreatment system comprising: a first exhaust gas flow pathreceiving a first portion of the exhaust gas from the combustion engine,the first exhaust gas flow path including an ammonia generator and aninjection port through which a reagent is injected into the exhaust gas;a second exhaust gas flow path receiving a second portion of the exhaustgas from the combustion engine and including at least one of a oxidationcatalyst and a particulate filter; a first selective-catalytic-reductioncatalyst receiving exhaust gas from the first and second exhaust gasflow paths; and a second selective-catalytic-reduction catalystreceiving exhaust gas from the first and second exhaust gas flow paths,the second selective-catalytic-reduction catalyst is a low-temperatureselective-catalytic-reduction catalyst.
 30. The aftertreatment system ofclaim 29, wherein the second selective-catalytic-reduction catalyst isdisposed downstream of the first selective-catalytic-reduction catalyst.31. The aftertreatment system of claim 29, wherein the first exhaust gasflow path includes an inlet disposed downstream of a turbocharger. 32.The aftertreatment system of claim 29, wherein the first exhaust gasflow path includes an inlet disposed upstream of a turbocharger.
 33. Theaftertreatment system of claim 29, wherein the injection port isdisposed downstream of the ammonia generator.
 34. The aftertreatmentsystem of claim 1, wherein the operating parameter is selected from thegroup consisting of: a temperature of the exhaust gas, a temperature ofthe combustion engine, a coolant temperature, and a runtime of thecombustion engine.
 35. The aftertreatment system of claim 12, whereinthe operating parameter is selected from the group consisting of: atemperature of the exhaust gas, a temperature of the combustion engine,a coolant temperature, and a runtime of the combustion engine.
 36. Theaftertreatment system of claim 16, wherein the operating parameter isselected from the group consisting of: a temperature of the exhaust gas,a temperature of the combustion engine, a coolant temperature, and aruntime of the combustion engine.
 37. The aftertreatment system of claim22, wherein the operating parameter is selected from the groupconsisting of: a temperature of the exhaust gas, a temperature of thecombustion engine, a coolant temperature, and a runtime of thecombustion engine.